Chromatic aberrations of diffractive waveplate optics for imaging applications can be corrected for different switchable states. Different opportunities for lenses and prisms, and their limitations are discussed.

The optical power of diffractive waveplate structures is limited not as much by fabrication technology issues as by the fundamental features of light propagation in complex anisotropic structures. The infinitely thin two-dimensional film approximation does not apply, and the efficiency of 4G lenses, prisms, etc., is reduced for geometries corresponding to sharp focusing lenses and large diffraction angles. Due to thin-film nature, these films can be combined to reduce effective focal length, increase effective diffraction angle, topological charge, etc. Along with this, we will discuss the opportunity of increasing optical power of 4G lenses, prisms, etc. without compromising efficiency.

We report about developing long-wave infrared diffractive optical components based on liquid crystals. The components show high efficiency and high transparency for the 10.6 &mu;m wavelength of CO<sub>2</sub> laser beam.

The fourth generation optics (4G optics) enables the realization of novel optical components (lenses, gratings, vector vortices, etc.) by patterning the optical axis orientation in the plane of an anisotropic film. Such components exhibit near 100% diffraction efficiency for wavelengths meeting half-wave retardation condition. In this framework, we have advanced a step-forward by realizing different diffractive waveplates (DWs) with arbitrary spatial patterns of the optical axis orientation by exploiting the capability of a Digital Spatial Light Polarization Converter (DSLPC). The DSLPC is based on a reflective, high resolution Spatial Light Modulator (SLM) combined with an “ad hoc” optical setup. The most attractive feature of the use of a DSLPC for photoalignment is that the orientation of the alignment layer, and therefore of the fabricated liquid crystal (LC) or liquid crystal polymer (LCP) DWs, can be specified on a pixel-by-pixel basis. By varying the optical magnification or de-magnification between the SLM and the alignment layer, the spatial resolution of the photoaligned layer can be adjusted to be optimal for each application. We show that with a simple “click” it is possible to record different high resolution optical components as well as arbitrary patterns ranging from lenses to invisible and even dual labels.

The thickness of functional layers in liquid crystal photonics devices is negligibly small compared to the substrates. New opportunities provided by multilayer 4G optical systems require minimizing the thickness of each layer. We report about our progress made by developing technology of thin flexible substrates, functional polymer films, solid electro-optical layers, and graphene oxide based electro-conductive coatings.

We present new lenses – waveplate lenses created in liquid crystal materials. Waveplate lenses allowed focusing and defocusing laser beam depending on the sign of the circularity of laser beam polarization. Using an electrically-switchable liquid-crystal half-wave retarder we realized switching between focused and defocused beams by the waveplate lens. A combination of two such lenses allowed the collimation of a laser beam as well as the change of focal length of optical system. Lenses of varied size and focal length are presented.

We have previously discovered a novel, facile approach to encapsulate ZnO nanorods within thiol complexes. This
approach results in a thiol uptake of 30-40% and a 400-500 nm thick thiol-Zn-thiol complex encapsulation layer
surrounding ZnO nanorods. By controlling experimental parameters, it is possible to control the thiol deposition,
enabling less uptake, which results in a surface monolayer instead of encapsulation. Through this approach, thiol
modification of other metal oxide materials, namely TiO<sub>2</sub>, Al<sub>2</sub>O<sub>3</sub>, and MgO, has been attempted. FTIR analysis indicates
that thiol adsorption occurs only on ZnO; chemisorption of thiols on other nanoparticles is not evident. Ultrahigh
vacuum single crystal adsorption studies demonstrate that ZnO(0001) is also more susceptible to thiol monolayer
formation, as evidenced by lack of methanethiol adsorption on TiO<sub>2</sub>(110) and MgO(0001). These results indicate that the
facile thiol modification approach opens a new avenue for surface modification of multi-component metal oxide
materials by enabling selective thiol modification of ZnO. This work has potential applicability for creating multiple
ligand-functionalized materials, which could be useful for the design of novel multiplexing sensors and photovoltaics.

The development history of polarization gratings (PGs), with origins in holography and Bragg gratings, accentuated and
reinforced their perception as gratings. We highlight their nature as waveplates - diffractive waveplates (DWs) - and
stress their family connection to vector vortex waveplates. This approach provides a straightforward understanding of
the unusual properties of PGs, such as nearly 100% diffraction in thin material layers, the presence of only one
diffraction order for a circularly polarized beam, wide diffraction bandwidth and the possibility of achromatic behavior.
With technology being ripe for applications such as beam steering, and optical switching, we characterize the resistance
of DWs to optical radiation, the effects of temperature and deformations. We also show that the boundary effects in the
manufacturing process make it necessary to use substrates larger than the desired aperture of the DW. The multicomponent
systems are discussed for developing normally transmissive switchable imaging systems, beam scanning, and
achromatic diffraction.

Nonlinear transmission is found to be significantly enhanced by introducing heavy metal atoms on the periphery of
macrocycle porphyrin complexes via rhenium selenide clusters that are coordinated to four pyridyl groups. Experiments
on 5, 10, 15, 20-tetra(4-pyridyl) porphyrin (H<sub>2</sub>TPyP), CuTPyP, [Re<sub>6</sub>(<i>&mu;</i><sub>3</sub>-Se)<sub>8</sub>(PEt<sub>3</sub>)<sub>5</sub>]<sub>4</sub>(H<sub>2</sub>TPyP)(SbF<sub>6</sub>)<sub>8</sub> (abbreviated as
P5H<sub>2</sub>TPyP), and [Re<sub>6</sub>(<i>&mu;</i><sub>3</sub>-Se)<sub>8</sub>(PEt<sub>3</sub>)<sub>5</sub>]<sub>4</sub>Cu(TPyP)(SbF<sub>6</sub>)<sub>8</sub> (abbreviated as CuP5TPyP) using 10 ns laser pulses at 523 nm
show that, in contrast to CuTPyP and P5H<sub>2</sub>TPyP, which are saturable absorbers at a low fluence of 1-100 mJ/cm<sup>2</sup> and
become nonlinear absorbers with a threshold larger than 1000 mJ/cm<sup>2</sup> at high fluence, CuP5TPyP exhibits an excellent
nonlinear transmission performance with a threshold as low as 20 mJ/cm<sup>2</sup>. A bulky rhenium selenide cluster was
coordinated to pyridyl groups in tetrapyridyl porphyrin. The modified copper (II) porphyrin complex CuP5TPyP has
strong nonlinear absorption at 523 nm and synergistic interaction between CuTPyP and P5H<sub>2</sub>TPyP is one of possible
mechanisms.

Nonlinear transmission upon the formation of an optically induced photonic band gap (PBG) is demonstrated by using
periodic layers of optical polymers doped with highly nonlinear transition metal oxides. The refractive indices of the
alternating layers are designed to be close and no PBG is formed at low power densities. Under high power illumination,
the index difference becomes large because of the high optical nonlinearities of the transition metal oxides.
Consequently, nonlinear transmission is accomplished with the formation and the broadening of the PBG. Compared to
typical optical limiters based on a PBG approach, our devices provide a large dynamic range and a broad operation
wavelength range. The experiments on a nonlinear Bragg mirror consisting of only 4 pairs of PVA:Co<sub>3</sub>O<sub>4</sub>-PVK, each
with a layer thickness of 85 nm, show a linear transmittance of greater than 50% throughout the visible, and nonlinear
transmission for a 10 ns laser pulse at 523 nm with a threshold of 30 mJ/cm<sup>2</sup> and a minimum transmission of about 10%.
The minimum transmission reduces to 5% for a 12-pair device. Improving the uniformity of each layer and adding more
pairs can result in even lower transmission at high intensities. The threshold can be further reduced through precise
design and control of the thickness of each layer. The device and material approach is promising for applications such as
protection for broadband detectors and human eyes.

The wide band gap and unique photoluminescence (PL) spectrum of nanocrystalline zinc oxide (nano-ZnO) make it
useful for a variety of photonics and sensor applications. Toward the goal of modifying the electronic structure and
optical properties of nano-ZnO, nanorods were functionalized with electron withdrawing organosilanes, 1H,1H,2H,2H-perfluorodecyltriethoxysilane
(PFDS) and pentafluorophenyltriethoxysilane (PFS), and a partially conjugated
heterobifunctional molecule, p-maleimidophenyl isothiocyanate (PMPI). Fourier transform infrared (FTIR) spectroscopy
and x-ray photoelectron spectroscopy (XPS) confirmed the presence of the modifiers on the nano-ZnO surface and
verified covalent attachment. PL spectroscopy was performed to evaluate the influence of the modifiers on the nano-ZnO
inherent optical behavior. An increase in the nano-ZnO near-band edge emission (UV) was evident for the organosilane
modifiers, despite their differing electronic structures, while the defect emission (visible) remained unchanged.
However, surface modification with the non-silane modifier PMPI resulted in unaltered UV and visible emission
intensity. The varying influence of the modifiers may be due to the absence of a silane group in the PMPI, allowing for
more efficient electron transport to the modifier. The influence of size/shape of the nanocrystalline ZnO was also
examined by reacting spherical nanoparticles with PFDS. Preliminary results indicate that PFDS modification of the
nanospheres resulted in similar PL behavior as the nanorods; although, the inherent PL of the spheres differs from the
nanorods. These studies will elucidate the role of modifier structure on surface-modified nano-ZnO optical behavior, so
that optical tailoring of the nano-ZnO inherent PL can be realized.

We study optical switching properties of novel azobenzene liquid crystal (azo LC) material systems based on mesogenic
azo dyes distinguished by enhanced absorption in the visible spectrum and a short lifetime of the photoexcited state. Due
to their mesogenic nature these azo dyes can be doped at high concentrations in room temperature LCs. This permits one
to obtain results using low energy density values required for observation of strong nonlinear optical processes and short
spontaneous restoration times of their original state. A photoinduced nematic-isotropic phase transition could be induced
with a single nanosecond pulse. Thin material layers of the order of radiation wavelength were used in the study.

The wide band gap and unique photoluminescence (PL) spectrum of nanocrystalline zinc oxide (nano-ZnO) make it
attractive for a variety of photonics and sensor applications. Toward the goal of modifying the electronic structure and
optical properties of nano-ZnO, the adsorption of 3-mercaptopropyltriethoxysilane (MPTES) has been investigated.
Nano-ZnO rods having widths of 10-20 nm and lengths of 100-300 nm were functionalized by ultrasonicating them in a
hot ethanol/water solution and adding MPTES. FTIR and X-ray photoelectron spectroscopy (XPS) of the modified nano-
ZnO confirm silane functionalization. The presence of hydroxyl groups prior to functionalization suggests that
adsorption to ZnO occurs primarily via a condensation reaction and the formation of Zn-O-Si bonds. Comparison has
been made to 3-mercaptopropyltrimethoxysilane (MPTMS) adsorbed in ultrahigh vacuum onto sputter-cleaned single
crystal ZnO(0001) in which MPTMS vapor is leaked into the vacuum chamber. In this case, bonding occurs via the thiol
groups, as indicated by angle-resolved XPS studies. Similar experiments in which sputter-cleaned ZnO(0001) is dosed
with dodecanethiol (DDT) confirm adsorption via S-Zn bond formation. Photoluminescence measurements of MPTES-functionalized
nano-ZnO show an increase in intensity of the UV emission peak and a decrease in the visible peak
relative to the unfunctionalized particles. The reduction of the visible emission peak is believed to be due to passivation
of surface defects.

Azobenzene liquid crystals (azo LCs) have been proven to possess the highest optical nonlinearity, bounding with photosensitivity, for cw laser beams. We show here that azo LCs are highly nonlinear for short laser pulses as well. Single as well as multicomponent room temperature nematic azo LCs were used in this study for single nanosecond pulses of the second harmonic of a Nd:YAG laser. These compositions demonstrate sensitivity starting from ~ 10 mJ/cm<sup>2</sup> and exhibit response time at the nanosecond scale. The effect of material composition, layer thickness and pulse
energy on the nonlinear response of a system of crossed polarizers comprising planar oriented LCs are reported.

Zinc Oxide (ZnO) is a wide bandgap semiconductor that has been the subject of considerable research due to its potential
applications in the areas of photonics, electronics and sensors. Nano-ZnO offers several advantages over existing biosensing
platforms, most notably a large surface area for greater bio-functionalization and an inherent photoluminescence
(PL) signal consisting of two emission peaks. One peak is in the UV, due to near band edge emission and the other is in
the visible (green) region, due to oxygen vacancies caused by crystalline defects. Real-time detection of surface binding
events may be possible if changes to the PL spectrum of a ZnO-based bio-sensor can be induced. Here we describe the
surface modification of nanocrystalline zinc oxide (nano-ZnO) to introduce chemically reactive functionality for
subsequent bio-functionalization. We have demonstrated through TEM-EDS that nano-ZnO powders have been surface
modified with a heterobifunctional organosilane crosslinking agent that contains an amine-reactive aldehyde group.
Furthermore, we have attached a fluorophore to the reactive aldehyde verifying the modified nano-ZnO surface is
available for subsequent biomolecular covalent attachment. The introduction of a chemically reactive modifier to the
surface of the nano-ZnO presents a template for the design of new, optically responsive bio-sensing platforms.

Carbon nanotubes were grown on silicon and quartz substrates in a honeycomb configuration using self-assembly nanosphere lithography and plasma enhanced chemical vapor deposition methods. Photonic nanoarrays were fabricated with varying spacing and carbon nanotube height. Both periodic and nonperiodic arrays were produced and evaluated. Optical properties of the arrays were studied and related to array geometry. Three dimensional diffraction maps were created that reveal the manner in which the nanoarrays interact with visible light. The unique optical properties of the arrays combined with the excellent mechanical and electrical properties of carbon nanotubes indicates that these materials may find many uses in the field of optoelectronics.

Carbon nanotubes (CNT) have been grown in a honeycomb configuration on silicon substrates using nanosphere self-assembly and plasma enhanced chemical vapor deposition. The optical properties of the arrays were also studied. Diffraction efficiency was found to be a function of the wavelength, angle of incidence and state of polarization of incident light. The unique optical properties of the arrays combined with the excellent mechanical and electrical properties of carbon nanotubes indicates that these materials may find many uses in the field of optoelectronics. In addition to their optical properties, periodic CNT arrays have a host of other unique electromagnetic and mechanical properties that may be exploited for numerous applications. Polarization measurements indicate that the intensity of both the diffracted light and diffusely scattered light is dependent on wavelength and angle of incidence. These arrays not only reflect and diffract light, but can also have a photonic band gap in, or around, the visible frequency range. The precise frequency location and size of this gap can be controlled by the structural and material parameters of the arrays.

A variety of novel ZnO nanostructures such as nanowires, nanowalls, hierarchical nanostructures with 6-, 4-, and 2-fold symmetries, nanobridges, nanonails have been successfully grown by a vapor transport and condensation technique. Doping both In and Sn into ZnO hierarchical nanostructures can be created. The 2-fold eutectic ZnO structures can also be created without any doping in the source. It was found that the hierarchical nanostructures can be divided into two
categories: homoepitaxial and heteroepitaxial where heteroepitaxy creates the multifold nanostructures. The novel ZnO nanowalls and aligned nanowires on a-plane of sapphire substrate have also been synthesized and the photoluminescence is studied. The ZnO nanowires also demonstrated very good field emission properties, comparable to carbon nanotubes. These nanostructures may find applications in a variety of fields such as field emission, photovoltaics, transparent EMI shielding, supercapacitors, fuel cells, high strength and multifunctional nanocomposites, etc. that require not only high
surface area but also structural integrity.

The nonlinear transmission of a combination of carbon nanotubes and nonlinear optical (NLO) dye is studied experimentally using nanosecond pulses. Multiwalled carbon nanotubes (CNT) are suspended in a solid matrix. The refractive index of the solid matrix is matched to a solvent/NLO dye solution. Evidence of both nonlinear scattering and nonlinear absorption is reported. Though there is evidence of increased scattering due to the CNT solid matrix, no enhancement in nonlinear response is observed.

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Journal of Applied Remote SensingJournal of Astronomical Telescopes Instruments and SystemsJournal of Biomedical OpticsJournal of Electronic ImagingJournal of Medical ImagingJournal of Micro/Nanolithography, MEMS, and MOEMSJournal of NanophotonicsJournal of Photonics for EnergyNeurophotonicsOptical EngineeringSPIE Reviews